Method of producing windings for electrical machines and appliances

Abstract

Windings for electrical machines and appliances, which windings remain mechanically stable even when the operational temperature is exceeded for a short period and ensure good heat transfer between the winding and the iron of the magnet core without additional impregnation, are produced by lining the slots in the magnet core with a slot liner coated on at least the side facing the magnet core with at least one B-state resin which is completely non-tacky at room temperature but is capable of being cured and becomes tacky at the temperatures employed in the curing of the thermosetting adhesive layer of the adhesive varnished wire used, by making the winding from adhesive varnished wire with a thermosetting adhesive layer and curing by heating the coating on the slot liner and the adhesive layer on the adhesive varnished wire.

We claim: 
     
       1. A method of forming windings on magnetizable cores for small electrical machines, wherein said cores have a plurality of openings for receiving said windings, said method comprising the steps in sequence of: (a) lining said openings with a slot liner formed of a material selected from the group consisting polyester sheet, laminates of polyester sheet and laminated fiber sheet, paper made from polyamide fibers, and asbestos paper, said slot liner being coated on at least the side facing the magnetizable core with at least one B-state resin which (i) is completely non-tacky at room temperature but (ii) is capable of being cured and of becoming tacky at elevated temperatures,   (b) randomly winding said core with a thermosetting adhesive varnished wire, and   (c) heating said wound core so as substantially simultaneously to cure said coating on said slot liner and said adhesive on said wire and to bond said liner to said core and said wire to said liner.   
     
     
       2. The method of claim 1, wherein said slot liner is coated on at least one side with a ketone-soluble resin which has a melting point of about 70° C, selected from the group consisting of a B-state epoxy resin and a phenolic resin. 
     
     
       3. The method of claim 2, wherein said resin comprises 40 to 20% by wt. rubber and 60 to 80% by wt. phenolic resin. 
     
     
       4. The method of claim 2 and further comprising a ketone-soluble rubber mixed with said resin. 
     
     
       5. The method of claim 4 wherein said ketone-soluble rubber comprises a butadiene/acrylonitrile copolymer. 
     
     
       6. The method of claim 4 wherein said resin is mixed with rubber in a ratio of 70:30. 
     
     
       7. The method of claim 1, wherein said slot liner is coated on at least one side with a polyurethane ester imide having (i) terminal isocyanate groups blocked by a monohydric phenol and (ii) free hydroxy groups, said imide being the condensation reaction product of (iii) a monohydric phenol, (iv) a polyester imide containing hydroxyl groups and (v) polyisocyanate, and (vi) a substantially linear epoxy resin containing secondary hydroxy groups and having a molecular weight greater than 30,000. 
     
     
       8. The method of claim 7, wherein said monohydric phenol is selected from the group consisting of phenol, cresol and xylenol, and said polyester imide comprises the N-carboxy-methylimide of trimellitic acid (I), triethylene glycol (II) and tris-(2-hydroexyethyl)-isocyanurate (III). 
     
     
       9. The method of claim 8, wherein components I, II and III are present in said condensation reaction product in the molar ratio I: (ii + iii) = 1:1.2 to 1:2   Ii: iii = 1:1 to 10:1   
     
     
       10. The method of claim 8, wherein said epoxy resin comprises a condensation product of epichlorohydrin and bisphenol A and has an average molecular weight in the range of 30,000 to 200,000. 
     
     
       11. The method of claim 10, wherein said epoxy resin has a hydroxy number of about 0.35. 
     
     
       12. A wound core for a small electrical machine and comprising in combination: a magnetizable core having a plurality of slots formed thereon,   thermosetting adhesive varnish coated wires randomly wound in said slots, and   a laminate of polyester sheet and fiber sheet lining said slots between said core and said wires, said laminate being coated with a B-state resin which (i) is non-tacky at room temperature but (ii) is capable of being cured and of becoming tacky at the thermosetting temperature of the adhesive varnish on said wire.   
     
     
       13. A wound core according to claim 11 wherein said coating comprises a ketone-soluble resin which melts at a temperature of about 70° C, said resin being selected from the group consisting of B-state epoxy resin and a phenolic resin. 
     
     
       14. A wound core according to claim 13 and further comprising a ketone-soluble rubber mixed with said resin. 
     
     
       15. A wound core according to claim 14 wherein said ketone-soluble rubber comprises a butadiene/acrylonitrile copolymer. 
     
     
       16. A wound core according to claim 14 wherein said coating comprises about 30% by weight rubber and about 70% by weight phenolic resin. 
     
     
       17. A wound core according to claim 12 wherein said coating comprises 40 to 20% by wt. rubber and 60 to 80% by wt. phenolic resin. 
     
     
       18. A wound core according to claim 12 wherein said laminate is coated on at least one side with a polyurethane ester imide having (i) terminal isocyanate groups blocked by a monohydric phenol and (ii) free hydroxy groups, said imide being the condensation reaction product of (iii) a monohydric phenol, (iv) a polyester imide containing hydroxyl groups and (v) polyisocyanate, and (vi) a substantially linear epoxy resin containing secondary hydroxy groups and having a molecular weight greater than 30,000. 
     
     
       19. A wound core according to claim 18 wherein said monohydric phenol is selected from the group consisting of phenol, cresol and xylenol, and said polyester imide comprises the N-carboxy-methylimide of trimellitic acid (I), triethylene glycol (II) and tris-(2-hydroxyethyl)-isocyanurate (III). 
     
     
       20. A wound core according to claim 19 wherein components I, II and III are present in said condensation reaction product in the molar ratio I: (ii + iii) = 1:1.2 to 1:2   Ii: iii = 1:1 to 10:1   
     
     
       21. A wound core according to claim 19 wherein said epoxy resin comprises a condensation product of epichlorohydrin and bisphenol A and has an average molecular weight in the range of 30,000 to 200,000. 
     
     
       22. A wound core according to claim 21 wherein said epoxy resin has a hydroxy number of about 0.35.